Metals such as chromium, cobalt, and manganese are used in corrosion, wear and high-temperature resistance alloys. Besides being expensive, metals of this type are not readily available nationally, thereby requiring stockpiling and importation. All of these factors result in a need for conservation of these metal reserves and resources which can be accomplished by more efficient utilization of existing resources and reserves.
One method of conserving metals of this type is to provide an alloy coating of a desired metal alloy on an underlying substrate in lieu of making the entire product of the desired alloy. Preparation of alloy coatings currently involves techniques such as physical vapor deposition (including evaporation, ion plating and sputtering), chemical vapor deposition, thermal spraying, and electrodeposition. Physical vapor deposition is the most versatile of these techniques, enabling the preparation of a large number of alloy compositions.
However, physical vapor deposition techniques have some disadvantage in that they require expensive, sophisticated vacuum, power and automatic control equipment in order to operate effectively. Additionally, physical vapor deposition coatings prepared on complex-shaped objects exhibit either poor line of sight coverage using an evaporation procedure or generally nonuniform thickness distribution using ion plating and sputtering techniques. All physical vapor deposition processes exhibit poor throwing power into deep recesses. Chemical vapor deposition has been shown not to be a practical process for depositing metallic alloys. It has been used most successfully in the preparation of semiconductor and insulator type coatings. The thermal spraying process has been used successfully in the deposition of numerous alloys but is not applicable for coating complex shaped objects or for plating into deep recesses.
The electrodeposition of cermet coatings has been disclosed in the prior art. This cermet technology involves the occlusion of a ceramic oxide, nitride, carbide, or boride in an electrodeposit to improve the oxidation or erosion resistance of the metal. Prior art patents disclosing cermet electrodeposition include the following: German Offer No. 2,611,857, Dec. 9, 1976 (Brown and Tomaszewski) "Electrodeposition of Particles Dispersed in Solution"; German Offer No. 2,217,778, Oct. 25, 1973 (Brown and Tomaszewski) "Cathodic Deposition of Small Water-Insoluble Particles on Metal Surfaces"; U.S. Pat. No. 3,745,098 (Brown and Tomaszewski). "Electrodeposition of Films of Fine Particles on Cathodes"; U.S. Pat. No. 3,061,525 (Grazen) "Method for Electroforming and Coating"; U.S. Pat. No. 3,672,970 (Tomaszewski) "Electrolytic Codeposition of Copper with Fine Particles"; and U.S. Pat. No. 3,666,636 (Tomaszewski and Tomaszewski) "Electrolytic Codeposition of Fine Particles With Copper."
In U.S. Pat. No. 3,892,637 (Polti), a hard and wear resistant coating is imparted to a finished article of copper by electrodepositing on the surface of the finished article a layer of a tin alloy containing antimony. This article is then heated to diffuse the base and coating metals into each other. The dispersing of a powder in a plating solution is also disclosed in U.S. Pat. No. 4,085,010 (Ishimori, et al.) and in U.S. Pat. No. 3,904,490 (Shigeru, et al). As disclosed in the Ishimori, et al., patent, a number of methods have been proposed to thoroughly disperse the powder in the solution including mechanical agitation of the coating bath, vibration of the object to be coated, and agitation of the bath with bubbles of air. The general use of heat treatment to effect a metal coating has also been disclosed in the following U.S. Pat. Nos.: 1,567,625 (Smith); 1,630,449 (Pilling); 3,505,181 (Marshall); and 3,755,090 (Jackson, et al).
Two other prior art articles of interest are the following: Kilgore, C. R., "Engineered Composite Coatings," Products Finishing, Vol. 27, No. 8, 1963, pp. 34-40; and Williams, R. V., "Electrodeposited Composite Coatings," Electroplating and Metal Finishing, Vol. 19, March 1966, pp. 92-96. These articles mention the possibility of forming alloys by codepositing a powder with an electroplate and the subsequent heat treatment of the coating to give an alloy composition. The former article suggests that a nichrome alloy can be produced while the latter suggests that an iron-nickel-chromium alloy can be produced. It has also been disclosed to electroplate a single metal alloy with the occlusion of a single metal powder. However, there was devised no reliable method for depositing an alloy coating of pre-determined composition on a metal base and particularly a ternary or greater alloy coating.